Automatic control device for a grinding machine

ABSTRACT

An automatic control device for a grinding machine comprising detecting means for detecting the grinding resistance of a grinding wheel, first control means actuated in response to the grinding resistance, and second control means for controlling the feed rate of the grinding wheel support to keep the grinding resistance constant in accordance with the actuation of the first control means. The automatic control device further comprises a timer set for a longer time period than the predetermined grinding cycle time period and energized at the same time as the start of the grinding operation, and embodies a relay energized to actuate a wheel dressing device after the timer is timed out and the wheel support is returned to its initial position.

United States Patent Kikuchi et a]. 1 Jan. 18, 1972 [54] AUTOMATIC CONTROL DEVICE FOR 2,802,312 8/1957 Gosney ...s l/l65.92 A GRINDING MACHINE 2,961,808 1 H1960 Dunigan ...5 l/l65.92 2,984,952 5/1961 Gebel ..5l/165.9 [721 lnvemrs= Sig 3,550,327 12 1970 Kusakabe et al ..51/l65.92

73 Assignee: Toyoda Koki Kabushiki Kaisha, Kariya Primary Examiner-Lester Swingle City, Aichi Prefecture, Japan Att0rneyHutchinson & Milans [22] Filed: Dec. 19, 1969 [57] ABSTRACT [2]] Appl' 886643 An automatic control device for a grinding machine comprising detecting means for detecting the grinding resistance of a [30] Foreign Application P i it D t grinding wheel, first control means actuated in response to the grinding resistance, and second control means for controlling Dec 25, Japan th feed e of th wheel pp to p the g ing resistance constant in accordance with the actuation of the first control means. The automatic control device further [58] S i 8 165 87 comprises a timer set for a longer time period than the o are 5 9 65 i 65 I 6 predetermined grinding cycle time period and energized at the same time as the start of the grinding operation, and embodies a relay energized to actuate a wheel dressing device after the [56] References cued timer is timed out and the wheel support is returned to its ini- UNITED STATES PATENTS Iial position.

2,168,596 8/1939 Hall ..51/165.9 X 13 Claims, 7 Drawing Figures mimsnmwmz' 3,634,974

SHEET 1 [1F 5 INVENTORS:

MAKOTO KIKUCHI and KUNIOMI HAYASHI lay (Q25; Mk/

Attorneys FIG. 3;

I INVENTORS:

. I MAKOTO KIKUCHI and I l I KUNIOMI HAYASHI v (Wat PATEmEnwamz 3534.974

SHEET 3 [IF 5 FIG. 5

Sqhmidt C|rcuit Schmidt Circuit} TLl 'P INVENTORS:

MAKOTO KIKUCHI and KUNIOMI HAYASHI Attorneys Sshmidt Electric I A Am ifier Current Schmidt Circuit SOL X 3| T U rp INVENTORS:

MAKOTO KIKUCHI and KUNIOMI HAYASHI Attorneys PATENTEDJANIBISTZ 3,634,974

SHEET 5 [IF 5 FIG. 7

INVENTORS:

MAKOTO 'KIKUCHI and KUNIOMI IIAYASIII WW/ZZM Attorneys AUTOMATIC CONTROL DEVICE FOR A GRINDING MACHINE BACKGROUND OF THE INVENTION The present invention relates to an automatic control device in a grinding machine.

Recently completion of grinding a workpiece with a high degree of accuracy and in a relatively short time period has come to be considered extremely important in increasing the efficiency of the grinding operation. Meanwhile, the demand for labor-saving devices is mounting. The conventional grinding machine has lacked a device for keeping the grinding resistance constant, that is, increasing the feed rate of the wheel support while the grinding wheel cuts well and stepping down this rate of feed as the cutting ability of the wheel is decreased. Thus, there has been a demand for an automatic control device which detects the grinding resistance, controls the feed rate of the wheel support in accordance with changes in this resistance in order to keep the resistance constant, and which embodies a timer which is set to operate from the start of the wheel support movement and will permit the grinding machine to proceed to the next grinding operation only when the present grinding operation is completed within the time set by the timer, and which will actuate a wheel-dressing device after the completion of the present grinding operation in the event that operation has not been completed within the set time period.

SUMMARY OF THE INVENTION It is a primary object of this invention to provide an automatic control device which controls the feed rate of the grinding wheel support in response to the cutting ability of the grinding wheel, to thereby maintain the grinding resistance of the wheel constant.

Another object of the invention is to provide an automatic control device which detects the grinding resistance through pressure differences in a control fluid.

A further object of the invention is to provide an automatic control device which detects the grinding resistance as strain on a tailstock center supporting the work.

A still further object of the invention is to provide an automatic control device which detects the grinding resistance through the medium of the electric current of a motor driving a grinding wheel.

Still another object of the invention is to provide an automatic control device comprising actuating means for moving a wheel support toward and away from the work, speed control means connected to the actuating means and having a passage hole and actuated in response to the grinding resistance of the wheel, thereby to regulate fluid flow from said actuating means to keep the grinding resistance constant.

A further object of the invention is to provide an automatic control device, wherein a wheel-dressing device is automatically actuated whenever the cutting ability of a grinding wheel is decreased and the feed rate of a wheel support is slowed down to where the time required for completion of the grinding operation exceeds a predetermined limit.

A still further object of the invention is to provide an automatic control device wherein the feed rate of a wheel support is controlled in accordance with the grinding resistance, and wherein the start of the wheel support movement energizes a timer set for a longer time period than a predetermined grinding cycle time, so that if a grinding operation is finished within the time set by the timer, the next grinding operation will follow, but in the event it is not finished at the expiration of the set time, the wheel dressing device will be actuated, but only after the present grinding operation has been completely finished.

BRIEF DESCRIPTION OF THE DRAWINGS The foregoing and other objects and effects of this invention will become obvious from the following description with reference to the attached drawings, in which:

FIG. I is an end elevational view of a grinding machine with parts broken away and shown in section;

FIG. 2 is a front elevational view of the grinding machine with parts broken away and shown in section;

FIG. 3 is a schematic diagram with parts in section of the hydraulic control circuit showing an automatic control device for control of the feed rate of the wheel support in one embodiment of this invention;

FIG. 4 is a detailed view, partially in section, of a grinding resistance detector;

FIG. 5 is a schematic diagram explaining an automatic control device for control of the feed rate of the wheel support involving another embodiment of this invention;

FIG. 6 is a schematic diagram explaining an automatic control device for control of the feed rate of the wheel support involving still another embodiment of this invention; and

FIG. 7 is a wiring diagram of the electrical control circuit for the dressing device of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIGS. 1 to 4, inclusive, illustrating an embodiment of this invention: 1 indicates the work held between a headstock 2 and a tailstock 3; 4 is a wheel support having thereon a rotatable grinding wheel 5 for grinding the work I; 6 is a feed cylinder for moving the wheel support 4', and 7 is a handwheel for manual feed movement of the wheel support 4.

A detector generally indicated as 8 for detecting the grinding resistance is provided with a clearance 60 between the inner periphery of a supporting end 10 of the tailstock 3 and the outer periphery of a tailstock center 9 carried by the tailstock, and with recesses 11, 11', and recesses 61, 61'. The recesses 11, 11' and 61, 61' are respectively oppositely disposed on the inner periphery of the supporting end 10. Pressure fluid, such as air, is evenly supplied to the recesses 11, 11' through lines I3, 13' and exhausted through the clearance 60 and the recesses 61, 61

When the cutting ability of the rotating grinding wheel 5 is decreased, the grinding resistance between the wheel 5 and the work 1 is increased, and as a result the load acting on the work I is increased. This increased load will cause the tailstock center 9 to be deflected in the direction of the arrow to the left, as viewed in FIG. 3. Thereupon, the flow passage of I the pressure fluid at the left-hand recess 11 is reduced and as a result the fluid pressure in the left recess 11 will be increased. On the other hand, the passage for the pressure fluid in the right recess 11' is widened to lower the fluid pressure in the recess 11'. The grinding resistance detector 8 picks up the grinding resistance of the wheel 5 as a differential fluid pres sure between the right and left recesses 11, I1, and the same pressure difference will now appear in the fluid flowing in lines I3, 13.

A switch valve 14 is actuated by the pressure difference developing between the lines I3, 13. The lines 13, 13' are connected to opposite ends respectively of a valve chamber 15, so that the pressure fluid may be supplied via throttles 36, 37 from a fluid supply passage and source I2. At the same time, the pressure fluid from the fluid supply passage 12 is also directly supplied to a central port I6 at the center of the valve chamber 15.

A spool valve 17, slidably mounted in the valve chamber 15, is normally biased toward the left by a spring 18 which is adapted to set the grinding resistance, and is provided with a central port 16 which under the conditions shown in FIG. 3 communicates with a right port 20. When, as described before, the fluid pressure in the left line 13 is increased and the pressure in the right line I3 is decreased upon an increase in the grinding resistance, the spool valve 17 will be moved to the right against the action of the spring 18 from the position indicated in FIG. 3. As a result of this movement a central valve land 19, carried by the spool valve 17, is shifted to make the central port 16 now communicate with a left port 20'.

Left and right ports 20, 20 of the switch valve I4, respectively communicate with the right and left ends of a control cylinder 21 via passages 22, 22. On a piston 23, slidably housed in the control cylinder 21, is formed a rack 24 which meshes with a pinion 25.

A feed rate control valve 26 for the wheel support constitutes a key to the speed control and is located in the pressure fluid circuit for the wheel support feed cylinder 6. A needle valve 27 in the feed rate control valve 26 is rotated together with the pinion 25 through suitable connecting means not shown. The valve 27 is moved in an axial direction upon rotation thereof through a screw-threaded portion 29 engaging an internally threaded portion of the valve housing 28 Thus, when the spool valve 17 in the switch valve 14 is shifted to the right from the position indicated in FIG. 3, permitting the fluid supply passage 12 to communicate directly with the left port 20, the pressure fluid flows into the right side of the control cylinder 21 through the passage 22', thereby moving the piston 23 to the left. Thus, the pinion 25 is turned counterclockwise, and the needle valve 27 is moved downward in the valve housing 28 by the screw-threaded portion 29, thereby throttling the passage hole or throat 30 in the fluid circuit controlling the feed cylinder 6.

A solenoid valve 31 is provided in the fluid circuit for the wheel support feed cylinder 6. In FIG. 3, a solenoid SOL of the valve 31 is deenergized to change the valve 31 to its right-hand position. At this position, the pressure fluid from a pump P is directed into the left end of the feed cylinder 6. The fluid at the right side of the feed cylinder 6 returns via the feed rate control valve 26 for the wheel support feed to a tank T. As the result, the piston 32 of the wheel support feed cylinder 6 is moved to the right. Thus, the wheel support 4 is moved forward, or toward the work 1, at the feed rate determined by the throttling position of the needle valve 27.

When the solenoid SOL of the valve 31 is energized to change the valve 31 to its left-hand position, the pressure fluid from the pump P forcibly opens a check valve 33 and, without passing through the wheel support feed rate control valve 26, directly flows into the right side of the feed cylinder 6, while the fluid in the left side of the feed cylinder 6 returns to the tank T. Thereby, the piston 32 is moved quickly to the left to return the wheel support 4 from the work 1 at a rapid rate. In FIG. 3, 34 is a knob for adjusting the elastic force ofthe spring 18 in the switch valve 14 to set the grinding resistance. 35 is a stop for the piston 23 provided in the control cylinder 21, and 38. 39 are throttle valves respectively.

So long as the grinding wheel 5 grinds well, the control valve 26 is opened to the maximum position and is maintained in that position until the grinding resistance, detected by the detector 8, increases to the maximum grinding resistance set by the spring 18, and accordingly the wheel support feed rate is relatively fast. As the cutting ability of the grinding wheel 5 decreases in use and the grinding resistance thus increases, the tailstock center 9 is deflected to the left in FIG. 3. Then, as stated above, the fluid pressure in the recess 11 and the line 13 will increase, while the fluid pressure in the recess 11' and the line 13' will decrease. When this pressure difference overcomes the force of the spring 18, the spool valve 17 of the switch valve 14 is shifted to the right against the spring 18. Thereupon, the pressure fluid in the fluid supply passage 12 will flow from central port 16 directly to the left port 20 and through passage 22 into the right side of the control cylinder 21, thereby moving piston 23 to the left. As mentioned above, the needle valve 27 is moved now downward to throttle the passage hole 30. As a result, the movement of the piston 32 in the feed cylinder 6 is retarded to decrease the feed rate of the wheel support 4, and accordingly the grinding resistance is reduced to the initial value. Thus with the grinding resistance not remaining at an increased value, the work 1 can be ground without developing undesirable strain.

FIG. 5 illustrates another embodiment of an automatic control device for controlling the feed rate of the wheel support according to this invention.

The outside surface of the tailstock center 9 is diametrically applied with a strain gage or meter 40, such as a semiconductor strain meter element, in the direction of the movement of the wheel 5. The output of the strain meter 40 is changed in response to the strain of the tailstock center 9. This output is transmitted via an amplifier and the Schmidt circuit to a motor 41 as a signal to run the motor 41 in either normal direction or in reverse direction. The needle valve 27 is connected to and driven by the motor 41. When the motor 41 is rotated in normal direction, the needle valve 27 is moved to the left in the valve housing 28 by virtue of the screw threaded portion 29, to throttle the needle valve opening and passage 30. If the motor 41 is rotated in reverse direction, the needle valve 27 is moved to the right to increase the needle valve opening and passage 30.

The position indicated in FIG. 5 shows the wheel support 4 in forward position. The pressure fluid from the pump P flows into the left side of the feed cylinder 6, while the fluid in the right side of the feed cylinder 6 goes through the wheel support feed rate control valve 26 and returns to the tank T. The piston 32 is shifted to the right to move forward the wheel support 4 at a rate depending on the degree of opening of the passage hole 30 of the wheel support feed rate control valve 26.

When the strain of the tailstock center 9 is small and the output of the strain meter 40 is low, a reverse-run signal is given to the motor 41 to open the passage hole 30 of the wheel support feed rate control valve 26 to a predetermined extent.

When the strain of the tailstock center 9 gradually increases to an extent where the output of the strain meter 40 exceeds a predetermined limit, a normal-run signal is given to the motor 41. Then the motor 41 is rotated in normal direction to move leftward the needle valve 27, thereby throttling the passage hole 30 until the output of the strain meter 40 is reduced below a predetermined limit.

Thus, while the grinding wheel 5 grinds well enough, the grinding resistance remains low, the needle valve 27 is kept open to the maximum and the wheel support feed is set at a high rate. If the cutting ability of the wheel 5 becomes poor, the grinding resistance is increased and the strain of the tailstock center 9 becomes large. Then, the motor 41 is rotated in normal direction to move to the left the needle valve 27. The passage hole 30 of the wheel support feed rate control valve 26 is throttled. The moving rate of the piston 32 in the feed cylinder 6 is thereby reduced and the grinding resistance is decreased. Thus, the work 1 can be ground without undesirable strain.

FIG. 6 illustrates still another embodiment of the automatic control device for controlling the feed rate of the wheel support according to the present invention In this Figure, a motor 42 is adapted to rotate the grinding wheel 5. The electric current in the motor 42 is metered and detected as a measure of the grinding resistance and changes therein are imparted to the motor 41 through the amplifier and the Schmidt circuit. When the grinding resistance is small and the electric current in the motor 42 is lower than a predetermined value, the motor 41 is rotated in reverse direction and the needle valve 27 is moved to the right to widen the passage opening 30. Thereupon, the moving rate of the piston 32 in the feed cylinder 6, that is, the feed rate of the wheel support, is increased. When the grinding resistance is increased, and the electric current in the motor 42 rises over the predetermined value, the motor 41 is rotated in the normal direction. Thereby the needle valve 27 is moved to the left to throttle the passage hole 30, and as a result the moving rate of the piston 32 in the feed cylinder 6 is reduced to thereby decrease the grinding resistance. This, the work 1 can be ground without undesirable strain.

FIG. 7 illustrates a diagram of an electrical control circuit for dressing the grinding wheel 5. A contact 43 is closed upon the signal to feed the wheel support 4. A relay 44, when energized, closes contacts 45, 46 and, when deenergized, will open these contacts. TR is a timer which is set for a longer time period than the predetermined grinding cycle time and closes a contact 47 when the preset time of the timer expires. A contact 48 is closed only when the wheel support 4 is at the extreme withdrawn position (the initial position) and is kept open while the wheel support 4 is moving forward during the grinding operation. A relay 49, when energized, closes contacts 50, 51 and, when deenergized, will open these contacts. D is a relay to control the dressing operation. With the relay D energized, contact 57, normally open, is closed. 58 is a normally closed contact and is opened upon the completion of the dressing control of the wheel dressing device 52 (H65. 1 and 2). A contact 53 is closed upon an automatic sizing signal issued from an automatic sizing device (not shown), when the work 1 has been completely ground. When energized, a relay 54 energizes the solenoid SOL of the solenoid valve 31 to withdraw the wheel support 4, at the same time opening a contact 55. Meanwhile, a contact 56 is closed when the wheel dressing device 51 is at its initial position, and is opened when the dressing device 52 is actuated.

Upon a forward signal issued with the wheel support 4 at its extreme withdrawn position, the contact 43 is closed to energize the relay 44 via the closed contacts 43, 55, to thus close the contacts 45, 46. Closing of the contact 45 holds the energization of the relay 44 through the closed contacts 45, 55, even when the closed contact 43 is opened. With the contact 46 closed, the timer TR is energized.

When the wheel support 4 is moved forward to start grinding the work 1 with the grinding wheel 5 cutting well, the grinding of the work 1 will be finished before the time set by TR expires, and the contact 53 will be closed by the automatic sizing signal. When the contact 53 is closed the relay 54 for withdrawing the wheel support is energized, and as the result the wheel support 4 begins to withdraw, while at the same time the contact 55 is opened. With the contact 55 opened the relay 44 is deenergized to open the contacts 45, 46 while the timer TR, without closing the contact 47, is returned to the deenergized position.

In response to a decrease in the cutting ability of the wheel 5, the device shown in FIGS. 3 to 6 is actuated to reduce the feed rate of the wheel support 4. Therefore, the time set by the timer TR expires before the grinding operation has been completed and thus the contact 47 is closed.

Upon the closing of the contact 47 of the timer TR, the relay 49 is energized to hold the contact 50 closed and at the same time acts to close the contact 51. At this time the wheel 5 is still working, with the wheel support 4 at the forward grinding position. With the contact 48 kept open, the dressing control relay D will remain deenergized even if the contact 51 is closed.

In this condition the grinding operation continues until the work I is completely ground to specified dimensions. When the grinding is finished, and the automatic sizing signal is issued to close the contact 53, which, when energized, energizes the relay 54 for withdrawing the wheel support 4, the wheel support 4 will be withdrawn.

When the wheel support 4 is withdrawn and returned to the initial position, the contact 48 is closed. Then the dressing control relay D is energized through said closed contact 51 to start the wheel dressing device 52 (FIGS. 1 and 2) to dress the wheel 5. At the same time, the energization of the relay D results in holding the contact 57 closed. Thus the dressing control relay D is not deenergized and therefore the control of wheel dressing is continued, even if the contacts 50, 51 are opened by the deenergization of the relay 49 through the open contact 56, which is opened by the actuation of the wheel dressing device 52. With the completion of the control for dressing the wheel by means of the wheel dressing device 52, the normally closed contact 58 is opened to deenergize the relay D.

As described above, this invention makes it possible to perform an efficient grinding operation at a feed rate matching the cutting ability of the grinding wheel. For this purpose a detector to measure the grinding resistance of the wheel is provided. This detector measures the grinding resistance during the grinding operation and in accordance with a change in the grinding resistance, the feed rate of the wheel support is controlled. Further, at the same time as the start of the grinding operation, the timer is energized. If the wheel cuts well and the work is finished before the timer TR is timed out, the next grinding operation will follow in normal manner. HOwever, when the cutting ability of the wheel is reduced and the feed rate of the wheel support is correspondingly slowed down, the grinding of the work will not as yet be completed when the set time of the timer expires. ln that case, the wheel support will be withdrawn but only after the completion of the present grinding operation and the grinding wheel will then be suitably dressed by the automatic wheel dressing device as described above. Thus, the dressing operation of the grindstone only occurs when needed. This is because the feed rate of the wheel support reflects fully the wheel cutting performance and its efficiency which are dependent on changes in the diameter and texture of the grinding wheel.

Meanwhile, the relay to start the wheel dressing device is energized only when the following two conditions are present, namely, the wheel support has returned to its extreme withdrawn or initial position and the set time has expired. Thus, even if the contact of the timer is closed, the dressing will be started only after the grinding of the work has been completed and the wheel has been withdrawn to its initial position. In this manner, there is no possibility of interruption in the grinding of the work before completion thereof.

We claim:

1. An automatic control device for a grinding machine comprising detecting means for detecting grinding resistance of a grind ing wheel,

first control means actuated in response to said grinding resistance,

actuator means for moving a wheel support toward and away from a workpiece, and

a speed control means for said wheel support actuator means and connected thereto,

said speed control means including a second control means connected to said first control means and a feed rate control valve connected to said second control means for controlling the feed rate of the wheel support responsive to said first control means, whereby the grinding resistance is kept constant throughout the grinding operation.

2. An automatic control device as claimed in claim I, wherein said device further comprises a timer set for a longer time period than a predetermined grinding cycle time and energized at the same time as the advance of said wheel support, and

a wheel-dressing control relay energized on condition that the set time of said timer has expired and the wheel support has returned to its original position.

3. An automatic control device as claimed in claim 1, wherein said detecting means includes a fluid source and fluid system which detects the grinding resistance of the grinding wheel in terms of pressure difference in the fluid, and wherein aid first control means is actuated in response to said pressure difference.

4. An automatic control device as claimed in claim 3, said device further comprising a timer set for a longer time period than a predetermined grinding cycle time and energized at the same time as the advance of said wheel support, and

a wheel dressing control relay energized on condition that the set time of said timer has expired and the wheel support has returned to its original position.

5. An automatic control device as claimed in claim 3, wherein said detecting means comprises a tailstock,

a tailstock center carried by said tailstock and deflected in response to the grinding resistance of the grinding wheel, fluid supply means,

means providing a clearance between the inner periphery of the tailstock and the outer periphery of the tailstock center,

a pair of recesses provided in the tailstock and diametrically opposed to said tailstock center in the direction of the movement of the wheel and supplied with fluid from said fluid source,

means for exhausting the fluid from said pair of recesses and clearance therethrough, thereby to produce a fluid pressure difference between the fluids of said pair of recesses, and wherein said first control means includes switch valve means actuated in response to said pressure difference and selectively distributing the fluid from said supply means,

said distributed fluid being supplied into said second control means for moving said feed rate control valve.

6. An automatic control device as claimed in claim 1,

wherein said detecting means comprises a tailstock center for supporting the work and deflected in response to the grinding resistance of the grinding wheel, and

strain meter means applied diametrically to the tailstock center in the direction of the movement of the grinding wheel, thereby to detect the grinding resistance of the wheel as strain of the tailstock center, and wherein said first control means comprises driving means driven in response to said strain imparted through a Schmidt circuit thereto and actuating said second control means.

7. An automatic control device as claimed in claim 1,

wherein said detecting means comprises electrical driving means for driving the grinding wheel, means to detect the grinding resistance of the wheel as a function of the electric current employed in driving said driving means, and wherein said first control means comprises a second driving means driven in response to said electric current imparted through a Schmidt circuit thereto and connected to said feed rate control valve.

8. An automatic control device as claimed in claim 5, said device further comprising a timer set for a longer time period than a predetermined grinding cycle time and energized at the same time as the advance of said wheel support, and

a wheel dressing control relay energized on condition that the set time of said timer has expired and the wheel support has returned to its original position,

9. An automatic control device as claimed in claim 6, said device further comprising a timer set for a longer time period than a predetermined grinding cycle time and energized at the same time as the advance of said wheel support, and

a wheel dressing control relay energized on condition that the set time of said timer has expired and the wheel support has returned to its original position.

10. An automatic control device as claimed in claim 7, said device further comprising a timer set for a longer time period than a predetermined grinding cycle time and energized at the same time as the advance of said wheel support, and

a wheel dressing control relay energized on condition that the set time of said timer has expired and the wheel support has returned to its original position.

11. An automatic control device as claimed in claim 5,

wherein said switch valve means comprises a switch valve housing,

a spool valve slidably mounted in said switch valve housing and having two reduced portions which are hydraulically connected to said control cylinder, and

a spring for urging said spool valve in one direction for connecting one of said two reduced portions with said fluid supply means, said fluid supply means being connected to said detecting means through both ends of said spool valve.

12. An automatic control device as claimed in claim 1.

wherein said second control means comprises a cylinder, and

a piston slidably mounted in said cylinder,

said piston having thereon a rack connected to aid feed rate control valve.

13. An automatic control device as claimed in claim 12,

wherein said feed rate control valve comprises a valve housing,

a needle valve threadedly engaged with said valve housing and operably connected to a pinion which meshes with said rack, whereby said needle valve is moved responsive to the movement of said piston in said second control means for controlling the flow rate of fluid into said wheel support actuator means. 

1. An automatic control device for a grinding machine comprising detecting means for detecting grinding resistance of a grinding wheel, first control means actuated in response to said grinding resistance, actuator means for moving a wheel support toward and away from a workpiece, and a speed control means for said wheel support actuator means and connected thereto, said speed control means including a second control means connected to said first control means and a feed rate control valve connected to said second control means for controlling the feed rate of the wheel support responsive to said first control means, whereby the grinding resistance is kept constant throughout the grinding operation.
 2. An automatic control device as claimed in claim 1, wherein said device further comprises a timer set for a longer time period than a predetermined grinding cycle time and energized at the same time as the advance of said wheel support, and a wheel-dressing control relay energized on condition that the set time of said timer has expired and the wheel support has returned to its original position.
 3. An automatic control device as claimed in claim 1, wherein said detecting means includes a fluid source and fluid system which detects the grinding resistance of the grinding wheel in terms of pressure difference in the fluid, and wherein aid first control means is actuated in response to said pressure difference.
 4. An automatic control device as claimed in claim 3, said device further comprising a timer set for a longer time period than a predetermined grinding cycle time and energized at the same time as the advance of said wheel support, and a wheel dressing control relay energized on condition that the set time of said timer has expired and the wheel support has returned to its original position.
 5. An automatic control device as claimed in claim 3, wherein said detecting means comprises a tailstock, a tailstock center carried by said tailstock and deflected in response to the grinding resistance of the grinding wheel, fluid supply means, means providing a clearance between the inner periphery of the tailstock and the outer periphery of the tailstock center, a pair of recesses provided in the tailstock and diametrically opposed to said tailstock center in the direction of the movement of the wheel and supplied with fluid from said fluid source, means for exhausting the fluid from said pair of recesses and clearance therethrough, thereby to produce a fluid pressure difference between the fluids of said pair of recesses, and wherein said first control means includes switch valve means actuated in response to said pressure difference and selectively distributing the fluid from said supply means, said distributed fluid being supplied into said second control means for moving said feed rate control valve.
 6. An automatic control device as claimed in claim 1, wherein said detecting means comprises a tailstock center for supporting the work and deflected in response to the grinding resistance of the grinding wheel, and strain meter means applied diametrically to the tailstock center in the direction of the movement of the grinding wheel, thereby to detect the grinding resistance of the wheel as strain of the tailstock center, and wherein said first control means comprises driving means driven in response to said strain imparted through a Schmidt circuit thereto and actuating said second control means.
 7. An automatic control device as claimed in claim 1, wherein said detecting means comprises electrical driving means for driving the grinding wheel, means to detect the grinding resistance of the wheel as a function of the electric current employed in driving said driving means, and wherein said first control means comprises a second driving means driven in response to said electric current imparted through a Schmidt circuit therEto and connected to said feed rate control valve.
 8. An automatic control device as claimed in claim 5, said device further comprising a timer set for a longer time period than a predetermined grinding cycle time and energized at the same time as the advance of said wheel support, and a wheel dressing control relay energized on condition that the set time of said timer has expired and the wheel support has returned to its original position.
 9. An automatic control device as claimed in claim 6, said device further comprising a timer set for a longer time period than a predetermined grinding cycle time and energized at the same time as the advance of said wheel support, and a wheel dressing control relay energized on condition that the set time of said timer has expired and the wheel support has returned to its original position.
 10. An automatic control device as claimed in claim 7, said device further comprising a timer set for a longer time period than a predetermined grinding cycle time and energized at the same time as the advance of said wheel support, and a wheel dressing control relay energized on condition that the set time of said timer has expired and the wheel support has returned to its original position.
 11. An automatic control device as claimed in claim 5, wherein said switch valve means comprises a switch valve housing, a spool valve slidably mounted in said switch valve housing and having two reduced portions which are hydraulically connected to said control cylinder, and a spring for urging said spool valve in one direction for connecting one of said two reduced portions with said fluid supply means, said fluid supply means being connected to said detecting means through both ends of said spool valve.
 12. An automatic control device as claimed in claim 1, wherein said second control means comprises a cylinder, and a piston slidably mounted in said cylinder, said piston having thereon a rack connected to aid feed rate control valve.
 13. An automatic control device as claimed in claim 12, wherein said feed rate control valve comprises a valve housing, a needle valve threadedly engaged with said valve housing and operably connected to a pinion which meshes with said rack, whereby said needle valve is moved responsive to the movement of said piston in said second control means for controlling the flow rate of fluid into said wheel support actuator means. 